Pericyte loss is the earliest pathological sign observed in diabetic retinopathy. Despite its importance in maintaining vascular function, the biology of pericytes remains poorly understood. Our goals are, first, developing tools to facilitate the studies of molecular and cellular biology of pericytes; second, investigating the effects of pericyte degeneration on the retinal vasculature.To ease the identification of retinal pericytes for profiling gene expression and characterizing cell-cell interactions, we have created transgenic mice expressing green fluorescent protein (GFP) under transcriptional control of the smooth muscle alpha actin (SMAA) promoter. The retinal blood vessels of these mice, including large vessels and capillaries, exhibit GFP fluorescence. Preliminary results indicate that both smooth muscle cells and pericytes are tagged with GFP. We are also establishing protocols to purify these live GFP expressing cells using a fluorescence activated cell sorter.To study the effects of pericyte degeneration, we have made transgenic mice overproducing human aldose reductase (AR) under control of the SMAA promoter. Tissue culture cells expressing high levels of HAR undergo apoptosis when grown in medium containing high galactose. This AR induced toxicity depends on the presence of galactose and can be inhibited by AR inhibitors. Since the endogenous AR activity of wild type mice is low, the AR toxicity will be limited to pericytes and smooth muscle cells in these mice on high galactose containing diet. As a part of NEIBANK project, we have made a normalized cDNA library from human pericytes and started a large-scale random sequencing of this library to catalogue genes that are differentially expressed in pericytes.